Acute and chronic stress produce a characteristic array of metabolic, endocrine, and behavioral changes in the mammal. Among these changes are increased secretion of glucocorticoid hormones from the adrenal glands, an inhibition of reproductive function, and a form of endogenous opiate mediated analgesia. In the human numerous disorders including depression, anorexia, alcoholism and chronic diseases are associated with these stress responses. A family of neuropeptides including adrenocorticotrophic hormone (ACTH), alpha melanocyte stimulating hormone (alphaMSH), and beta-endorphin derived from the precursor protein proopiomelanocortin (POMC) are essential chemical mediators of the stress response. POMC is first produced in specialized neurons of the brain and in pituitary cells at critical points in development of the brain and endocrine glands suggesting that PMOC also plays an important role in regulating the growth and differentiation of these tissues. The goal of our project is to understand the physiological role of each of the peptides derived from POMC in the normal development of the neuroendocrine systems and in the regulation of the neuroendocrine responses to stress. To accomplish this goal, we will create loss of function mutations in the POMC gene by homologous recombination in embryonic stem cells and use these cells to subsequently generate chimeric transgenic mice by blastocyst injection. The resulting mice will carry mutant POMC alleles that either block the production of all functional POMC peptides or that result in a selective loss of beta- endorphin(1-31). Homozygous POMC gene mutated mice will be analyzed throughout prenatal development to characterize the effects on neuroendocrine cell proliferation and cytodifferentiation. These developmental studies will focus on the paraventricular and antero- ventral periventricular nuclei of the hypothalamus because they are nodal points of the central circuitry controlling the hypothalamic-pituitary- adrenal and hypothalamic-pituitary-gonadal axes, respectively. The beta- endorphin deficient mice are expected to survive into adulthood and will be used to determine the role of centrally produced beta-endorphin in the modulation of the hypothalamic-pituitary axis under basal and stress conditions and in the expression of stress-induced analgesia. In the future, our molecular genetic approach will also be applied to produce mice carrying POMC alleles mutated in such a way to prevent the production of alphaMSH or mutated alleles for specific POMC peptide receptor subtypes to prove the physiological function of each of these molecular components of the mammalian stress response.